Segmented cages of the above-mentioned type are commonly used in certain types of rolling-element bearings, especially in large bearings. Two or more rolling elements are housed in each rolling-element bearing cage segment. The cage segments are configured to guide the rolling elements while maintaining a defined circumferential spacing of the rolling elements relative to one another and to accelerate the rolling elements if they are located in a load-free zone of the rolling-element bearing. For example, designs are known in which four rolling elements (rollers or also balls) are received in a cage segment and guided by the cage segment. These cage segments can be made of plastic, but even when plastic is used, the combined weight of the cage segment and the rolling elements it contains can exceed 10 kg.
Circumferential clearance must be present between the cage segments in order to maintain proper functioning of the bearing and also due to manufacturing tolerances. This clearance may range from a few millimeters up to a few centimeters. Under certain load conditions a cage segment filled with rolling elements in a load-free zone of the bearing may collide with an adjacent cage segment. The collision creates high impact forces and corresponding stresses. Accordingly such collisions create high loads on the cage and its segments, and this can lead to breakages and early bearing failures.
The impact load on the entire cage depends on how strongly each rolling element retained by the cage impacts against a cage bridge directly in front of it in a direction of movement. If one cage segment collides with a cage segment in front of it, the following can happen.
First the trailing cage segment can impact against the outer surface of the last cage bridge of the cage segment directly in front of it. This causes the trailing cage segment to decelerate.
When the trailing cage segment stops, the rolling elements in that cage segment continue to move due to inertia and impact against the cage bridges immediately in front of them in the direction of movement. The rolling elements in a given cage segment may be located different distances from the bridge that is ahead of the rolling element in the movement direction. Accordingly all of the rolling elements can impact an upstream cage bridge at the same time or at different times. If four rolling elements are present per cage segment, for example, the impact forces experienced by the cage segment may be up to four times greater than the impact force produced by a single one of the rolling elements impacting against a cage bridge. Accordingly the structure of the cage segment must be designed for the greatest anticipated load, i.e., for the load experienced when all rolling elements impact on an upstream cage bridge at the same time.
Furthermore it has been found that the force or shock produced by rolling elements impacting a given cage bridge is also transmitted to the entire cage, i.e., from cage segment to cage segment and to cage segments other than the one holding the impacting rolling element. Disadvantageously, this may produce unwanted vibrations and a rough or noisy operation of the rolling-element bearing. Furthermore, the material of the cage or of its segments is subjected to a correspondingly high load.
The known remedies for reducing impact load are not entirely satisfactory. First circumferential clearance may be reduced. However, the ability to reduce clearance is limited by production methods and the costs associated with maintaining a small clearance. The mass of each cage segment can also be reduced. However, this reduces the overall load capacity of the rolling-element bearing. It is also sometimes possible to reduce or avoid the load-free zone, but this is not always possible.